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E. THOMSON HIGH FREQUENCY INDUCTION KPPARATUS Filed April 25. 1924 2 Sheets-Sheet lllllllllllllllllllll' E//hu Thomson, @y WMA fnl/en o/ Hfs #ta/'nef Patented Sept. 4, 1928.

UNITED STATES PATENT oFFicE.

ELIHU THOMSON, OF SWAMPSCOTT, MASSACHUSETTS, I TRIC COMPANY, A CORPORATION 0F ASSIGNOR TO GENERAL ELEC- NEW lYORK.

HIGH-FREQUENCY INDUCTION APPARATUS.

Application filed April 25, 1924. Serial No. 709,045.

f eiated by apparatus containing resonant or oscillating circuits and the frequencies employed have been of the order of one hundred kilocycles or higher.' The generation of these very high frequencies has'involved the'use of spark discharge gaps or vacuum tubes.

Vacuum tubes are relatively fragile and subject to deterioration with continued use. Dynamo electric machines on the other hand are rugged and capable of continued usewith little depreciation. For relatively' .Y large power outputs vacuum .tube outfits occupy far more space than dynamo electric iriachines. i

ln accordance with my invention the advantages of the ruggeduess. dependability and coinpactness of a mechanically operated source of power are secured for high frequency heating devices.

'.llic accompanying drawings illustrate an embodiment of my invention. Fig. 1 is a somewhat diagrammatic representation of a complete heating outfit; Figs. 2 and 3 respectively are longitudinal and cross sections taken vertically through a dynamo which is suited for the purposes of my invention and Fig. 4t is a view illustrating a detail of the dynamo structure.

F ig. 1 shows a dynamo electrical machine 1 combined in operative relation with a high frequency primary inducing coil 2, within which is arranged a 'refractory Crucible 3 containing a charge 4 of materials to be heated. This crucible may be supported upon the dynamo electric machine by pedestals 5, 6. The Crucible 3 may consist of conducting material, as for example carbon or tungsten. Between the crucible 3 and the coil 2 a re- `heat losses.` electrical machine 1 will fractory insulating layer? is provided. A refractory,

non-conducting cover 8 reduces The construction of the dynamo be more fully described in connectioniwith Figs. 2, 3 and 4.

' is ofthe type delscribed `in my prior Patent No. 432,655 of uly .22, 1890. 'A dynamo of this construction is shown in Fig.1'surrounded by a jacket 9, through which Water or other cooling fluid .maybe circulated. Preferably the samie cooling fluid is also circulated through the primary winding 2 which consists of convolu- .tions ofva hollow conductor such as flattened copper. formed into a'helix as shown. This lieliir is lconnected by conduit 10, l1 and 12 understood in automobile practice. The cooling Huid Zmay be introduced bv a funnel l5 rovided i 'tl Cock 15,. y p Wi i a stop Theclosed system for circulating the coolthe coils may be arranged to "et a variable self-induction. lVlien the current of both helices is in the same direction the reactance is a maximum and when the inner coil is reversed in position so that its turns have currentiin the opposite direction to the current in the outer coil, the reactance is of minimum value. The condenser 18 need not be of unusual high capacity, as it is used for regulating purposes.

The dynamo is excited by a shunt Wound generator 20, the field coils 21 of Which are ance ivith the connected in series with the variable resistance 22. 'l`he exciter circuit 23, 23' is connected to the field terminals24g'24. `A onductor 25`co1ii`pletes the field circuit.' If desired the exciter 2O may be regulated to over excite the generator l vso as to assist the condenser 1Sv to secure the des'i'r'edlh'igli pv'e" factor. The dynamo'l mafs,t be'drTve'iibtrv bine, motor or any suitableh sort of4 power which will give it a periodic'it)-n suit-aliento' the furnace desired which ordinarily wigllfbef vithin the range of l0v to 20 kilocycles, al-

thouglrfor some-purposes the'requency' may be somewhat belovv or above this range.

'lhe type of .dynamo outlined in Fig'. 1 shows the greater detail iniFigs. .2 andf-'ahd is vparticularly adapted to sbe inadethe means for generatingeiciently high frequency cu'rrents, particularly ofsuch frequencies asare suitable for the operation .of liighfr'equeny induction furnaces. 'lhe revolv-ing'streture QS preferably is Igiven* manypoles, for rexaniple about 100 .or more. The` stationary structure 29 has its conductors 30 plated iii slots which are double. the number. of' the poles, that is 200 or more, .the clearance being made as small as possible between these two structures. The armature' conductors' 30Ya1'e connected in series,\in'multipla-in multiple series groups or other desired relationf depending on theV voltage required -inaccordell understood practice.

-A part of the revolvingmiddl polar portion 2,8v is represented in cross section"ih'-Fil1. 3' with the polar notches partly exposed. Fig. ll-shows an elenientof-y the laminated polar iron portion 31 and the support/ ing platel outside thereof indicatedat'Q:l 'This plate 32 is made of Ahigh resistance metal, such as chromesteehnichroine or thel like and forms afflange 33 which extends outward to the edge ot' the revolving part-and'is'not brolren or toothed but complete in outline. 'l`his construction prevents extreme air agita'L tionand reduces the noise. The plate BZIay be replaced b v a more massive "plate of highly conducting material, such as copper, in which case slight variations of the'niagnetie field nearby are smoothed out` without being the cause of muchloss of' energy. There- \ol\'ing structure is surrounded b'y the armature laminations 34. These laminations are mounted en the inner periphery of the cas; ing 35 which is closed except foro'penings'for the terminals 36' which are sealed 4therein as indicated by insulating'Y bushings 3T.- Thus the machine becomes'a relatively noiseless, self-contained, high frequencyv dy'nanio o good eiiciency capable oi' producing cur'rent of such frequencies as-are required for the operation offurnaces of the type shown for example, in Northrup Patent No. 1,286,395.

lVhat l claim as new and desire to secure by Letters Patent of the United States is: 12* i An electric heating apparatus comprischine eapable of delivering alternating current ofla periodicity of about tentotvventy imcyaiefiefj ree-ad, a' pas@ massig iviiding coitedtio said source and consti-ictecl to fp erm itL electromagnetic interlinkage wftha load to be heated without interlinkage with; a magnetic core, a variable reactance connected in the electric circuit in sries v'vithv said dynamo-electric machine" and saidfnindhiggandgcommonCOOIinganeanSOr said dynamo-electric nacliinefandsai'd winding.-

2. Arr elect-ric heating apparatus? vcompiisingthe combination of'a dyaInd-electri machine capable of delivering: alternating current of a5 periodicity of: at` leilst'a'bout ten kiloeycles per second', an'air cor transformer winding 'operatively 'conne' i thereto whereby energ from said-machine mayv be induced ina' loadto: be-heatedfa' variable'reactance connect'edl in` the .eledtric circuit in Series 'with' said dynamolelectiicnla'cl'iineand saidwindingyzindcommoricoolingmeans or said dynamo-electricmachinezairdsaith Winding.f V-

3.- "Anelectric heatihg apparatus l'compris'- ing the' eofnbiriatioh of# 1r ,dyn'hxn'of electric machine whiehis 'capable ovdlivrihgvalternating current.: at periodicity' 'ofv about 'ten to; ttventykilocyclesr per secorid,"'a"` jacket thereforl wherein a-co'oling fluid'r'nay be'cir'- cu'lated, a'^primaryinddcingcoil comprising hol-low' conductors," c'nduitsr'crmeetin g Said inducing coil toA said'jacketitopermitthe intercircultionof a: coo'lihg'fluid', a'radiatr included in series with said conduits, electric conductors electricallyl connectiirgfsaid inducing coil to said:machineglaniw variable condenser included in said connections,

4. An india-'tion furnace heating system comprising a dynamo-electric machine, a heating coil free from interlinkage of transformer iron, electrical connections between said dynamo-electric'machine airidsaid coil, and a variable condenser included in said'con'- nections in series with saidcil and said dynamo-electricmachine.

5. An induction furnacev heating system comprising a.' dynamo-'electric machine, a heating coil free from interlirlrage'of tra'nsformer iron', electrical connections between s'aid dynamo-electric machine ands'aid coil, aiva'riable condenser'included in'said'connections, and a variable' inductan'ce' included in said connections. g I A Y In Witnesswh'ereof,l have'hereunto set my han'd this tiventy 'first dayo'f 'A `ril, 1924.

EIJIHUvl OMSON 

